OBJECTIVE: To determine whether a sensitive period exists for prenatal stress effects on primate behavior and physiology. RESULTS In a prospective longitudinal study, infants from undisturbed pregnancies (controls) are compared with infants from females stressed during early gestation (Days 45 - 90 postconception) or during mid-late gestation (Days 90 - 145 postconception). Infants are compared on measures of birth weight, early neuromotor development, cognitive development, social behaviors, and behavioral and endocrine responses to challenge. Our results have indicated that early stress significantly reduced birth weight relative to mid/late stress and early stress was more potent in disrupting neurobehavioral development compared to mid/late stress and undisturbed controls. FUTURE DIRECTIONS Studies will determine (1) whether a sensitive period exists for the prenatal stress effect; (2) whether there are interactional effects of prenatal stress with maternal emotionality and maternal exposure to alcohol; and (3) whether the effects persist into adolescence. KEYWORDS neonatal, neurobehavior, cognitive development, social behavior, sensitive period, critical period, developmental disabilities, endocrine responses, neuromotor, memory and learning, WGTA testing